I. Field of the Disclosure
The technology of the disclosure relates generally to flash-memory-based storage in mobile computing devices.
II. Background
Flash memory is a non-volatile data storage medium to which data may be electronically written and erased. Flash memory is presently used in a variety of flash-memory-based storage devices, including memory cards, solid-state drives, and Universal Serial Bus (USB) flash drives. Flash-memory-based storage devices may offer fast read and write times comparable to dynamic Random Access Memory (RAM) while providing higher durability and shock resistance than conventional hard disks.
To facilitate the widespread use of flash-memory-based storage devices, a number of standards have been developed or are currently under development. One such standard is Universal Flash Storage (UFS), developed by the Joint Electron Device Engineering Council (JEDEC) for flash-memory-based storage in mobile computing devices, such as smart phones and tablet computers. UFS adopts the Small Computer System Interface (SCSI) Architecture Model and command protocols supporting multiple commands with command queuing features, thus enabling a multi-thread programming paradigm. Another standard developed by JEDEC is the Embedded MultiMediaCard (eMMC) standard, which offers a simplified application interface design, small package sizes, and low power consumption. eMMC flash-memory-based storage devices are presently one of the primary forms of storage in mobile devices.
Conventional flash-memory-based storage device standards such as UFS and eMMC are currently designed for management and usage by a single input/output (I/O) client. However, many modern computing devices are capable of supporting multiple I/O clients (e.g., hosts or other processor subsystems) simultaneously using virtualization environments. In such virtualization environments, multiple I/O clients may each need to interact with a single flash-memory-based storage device as if it were the only host of the flash-memory-based storage device. Similarly, the flash-memory-based storage device may need to operate as if it is communicating with only a single I/O client, when, in fact, it is communicating with multiple I/O clients.
In particular, when flash-memory-based storage standards are extended to a multi-host environment, the flash-memory-based storage device must be able to maintain effective power control while supporting multiple I/O clients. In conventional flash-memory-based storage devices interacting with a single host, power control is relatively simple, in that the single host alone controls a power state of the flash-memory-based storage device. However, to achieve effective power control in a multi-host environment, a flash-memory-based storage device may need to transition between power modes in response to receiving requests from multiple hosts, as opposed to a single host.